The art of transmitting and receiving intelligence by using short-range two-way radio communication systems is well known in some industries, and has, for example, gained wide-spread recognition by the fast food restaurant industry. In fast food restaurants, or such other similar commercial establishments, orders are generally placed by the customers, either in person, or at a remote location. The remote customer location is provided with a microphone and a speaker to establish a two-way communication link with the operating personnel executing the order. The microphone and speaker are usually connected by a metallic line to a base station, which receives and transmits the customer's orders over a radio frequency link, to several remote stations or units, for execution.
When, on the other hand, the customer places the order in person, an operator on the restaurant premises transmits the order to the base station and to the several remote stations for execution. Thus, whether the orders are placed in person, or at the remote customer location, they are communicated to the base station, which in turn relays such orders to the remote stations.
Each one of the remote stations generally includes two circuit activating buttons. One button enables the user to communicate exclusively with other users, and the other button enables the user to communicate with the customer. The principal disadvantage is that the system requires two distinct radio frequencies to operate in a duplex mode. The second disadvantage of the conventional two-way radio frequency communication system is the interference caused by other nearby radio communication devices, and by the existing electrical system, such as lighting and power systems. Another disadvantage is the burdensome licensing requirement from the Federal Communications Commission.
Therefore, it would be highly desirable to have a new and improved communication system which reduces substantially, if not eliminates totally, the interference with the surrounding power and radio systems and the two frequency requirement. The communication system should be available for use without any licensing requirement from the Federal Communications Commission.
Several solutions have been attempted in the field to overcome the foregoing problems associated with the use of the radio frequency communications systems. For instance, the U.S. Pat. Nos. 2,404,696, 2,421,468, 2,494,645, 2,599,368, 3,501,640, and 4,229,829, describe various optical communication systems to replace the conventional radio systems. Such optical communication systems may be suitable for use in particular applications, since optical systems do not require government licensing due to the fact that no electrical interference is created by the use of such systems. However, none of the prior known optical communication systems have been entirely satisfactorily adapted for use in fast food restaurants or for relatively inexpensive short range two-way communication systems in general.
The conventional optical atmospheric transmission systems generally utilize a 95 KHz subcarrier frequency which is modulated by the audio signals. The subcarrier frequency then amplitude modulates the optical emitters. The conventional duplex optical transmission systems generally utilize two different operating optical frequencies of the modulated light beam, in an attempt to prevent interference between the transmitted and the received modulated light beams.
The use of dual operating optical frequencies requires relatively expensive components, such as emitters and receptors, and therefore increases the cost of the communication system. In this regard, the modulation of the beams over long wavelength carriers requires a sufficient spacing between the emitters and the receptors for minimizing the interference therebetween. However, the optical system is rendered relatively bulky, expensive and impractical to carry when two different frequencies are utilized.
At the present state of the art, long wavelength optical components (emitters and receptors) are very expensive and not conducive to be used in a lightweight economically priced system. High-Q filters have been utilized to discriminate and to reduce the interference between the transmitted and the received signals. However, the problems associated with the use of high-Q filters reduces the transmission efficiency and render such solution unduly costly. In this respect, the high-Q filters are not only relatively expensive, but they are also generally sensitive to the input voltage and to the ambient temperature. Thus, the conventional communication systems utilizing high-Q filters require frequency stabilization circuits for the transmitted signals, thereby adding unnecessarily to the cost of manufacture of the system.
Therefore, it would be highly desirable to have a new and improved relatively inexpensive to manufacture, short range communication system, which can be used for commercial establishments, such as for use in fast food restaurants. The communication system should be a full duplex system which avoids the foregoing licensing problems associated with the prior known radio frequency systems. The portable duplex communication system, should be relatively stable and inexpensive to produce, to operate and to maintain.
The conventional optical communication systems have a relatively poor transmission efficiency, and thus a higher power requirement is necessitated to compensate for the signal to noise ratio. Such high power consumption causes the power source, such as a battery, to be drained prematurely.
Therefore, it would be highly desirable to have a new and improved communication system which has a relatively high transmission efficiency, and a low power consumption, for preventing rapid drainage of the power source.
Another problem associated with the conventional optical systems is the increased loss of sensitivity, at the base station, as well as at the remote stations, which is caused primarily by leakage of the optical signals from the emitter to the adjacent receptor. Such leakage interferes with the proper reception and recognition of the signals and affects adversely the sensitivity of the communication system. An attempted solution to resolve such leakage problem is disclosed in U.S. Pat. No. 2,404,696, whereby an opaque light shield is disposed between the transmitter and the receptor of the communication device.
Such solution has proven to be clearly less than totally satisfactory for use in fast food restaurants, where portable remote stations are transported constantly by the operators. In this regard, the recommended communication device requires the alignment of the stations, so as to prevent the interposed shield from interfering with the light propagation path. However, it is not practically feasible to maintain continuously a straight radiation path between the stations, particularly in an intercom system for use in fast food restaurants, or other business establishments, such as business offices, where movement of personnel is required or otherwise important to the proper functioning of the business.
Therefore, it would be highly desirable to have a new and improved communication system which has minimal sensitivity loss, and which reduces substantially, if not eliminates completely, the leakage between the transmitters and the receptors of the base station and the remote units. The communication system should be amenable to continuous transportation by the users.